The worldwide recalls of Toyota, Nissan and Honda vehicles over defective air bag systems are going to inconvenience thousands of U.S. motorists.

Just the Toyota scope alone is impressive.

In the U.S., the automaker will be forced to go on the hunt for defects in 170,000 vehicles. Even worse, Toyota says it may have to inspect 510,000 vehicles in order to pinpoint those that have the mistakes. Vehicles involved include certain Toyota Corolla, Corolla Matrix, Sequoia, and Tundra, and Lexus SC 430 models manufactured from 2001 to 2003.

Even before Thursday's announcement, Toyota and Honda had announced the recall of 1.5 million vehicles this year over faulty air bags. Last year, there were 22 recalls involving air bags spread across 18 brands. And the problems aren't isolated to the U.S. In Thursday's recall, Toyota, Honda and Nissan will need to track down 3 million vehicles around the globe.

Faulty air bag systems are emerging as automakers' biggest nightmare when it comes to recalls, far from their purpose of saving lives in accidents.More problems crop up as automakers find ways of adding more air bags to cars, find new places to put them and make them more sophisticated. The cause of the recalls run the gamut from faulty circuitry to missing cover rivets.

In Thursday's recall, Toyota blames a manufacturing defect for the problem. The system could have defective "propellant wafer" that could cause the inflator to rupture and the front passenger air bag to deploy abnormally in the event of a crash.

Air bag systems are enormously complex. The bags have to correctly deduce whether a vehicle has been struck in an accident, inflate and then deflate bags in milliseconds -- skipping those where seat detectors deduce a passenger is too small and may be injured by the bag itself.

Computers make the instant decisions, and they can be faulty. "You are relying on millions of lines of codes to make decisions within milliseconds," Washington-based car safety expert Sean Kane told USA TODAY in February. With all the snafus, some air bags hold the potential to "create more injuries than they can prevent."